1. Field of the Invention
This invention generally relates to laser modules, control methods of the same, control data, and control data generation methods, and more particularly, to a laser module that keeps an optical output intensity constant, a control method of the same, control data, and a method of generating the control data.
2. Description of the Related Art
In recent years, in the fields of optical communication and home appliances, semiconductor lasers are for use in various products. In particular, with respect to the laser module having a semiconductor laser, there is a need for maintaining a constant optical output intensity, output from the laser module.
A description will now be given of a semiconductor laser module having a wavelength locker (conventional art), which is used for optical communication, as an example of the conventional semiconductor laser module. The semiconductor laser module having the wavelength locker is a laser module that outputs a light having a given number of different wavelengths (lock points). There is a demand for outputting a given wavelength (lock point) at a given optical output intensity with accuracy. FIG. 1 is a block diagram showing the semiconductor laser module having the wavelength locker. FIG. 2 schematically shows a package from which a lid is partially removed.
A semiconductor laser 10 is provided on a substrate 38. A light output from the semiconductor laser 10 passes through an output optical system 12, and is then output to the outside of the module, which corresponds to an external output system 90. The substrate 38 shown in FIG. 1 corresponds to a reference numeral 86 in FIG. 2. The semiconductor laser 10 shown in FIG. 1 corresponds to a reference numeral 81 in FIG. 2. The output optical system 12 shown in FIG. 1 corresponds to a reference numeral 82 in FIG. 2. An optical output intensity 50 denotes an optical output from the module to the outside. The output optical system 12 is an optical apparatus provided between the semiconductor laser 10 to a light extracting portion. For example, in a case where the light extracting portion is an external optical system 90 connected with an optical fiber as shown in FIG. 2, there may be provided a lens that couples the semiconductor laser 10 and the external optical system 90 and a beam splitter for preventing the light reflection. However, in some cases, the beam splitter may not be used.
A temperature setting apparatus 32 sets the temperature of the semiconductor laser 10. As shown in FIG. 2, a thermoelectric coller (TEC) 88 is provided. The beam emitted to the rear side of the semiconductor laser 10, which is arranged on an opposite side of an optical output side, passes through a beam splitter 14 and is split into two. One of such split beam reaches a light receiving element 16, which corresponds to a reference numeral 85 shown in FIG. 2. At this time, a monitor optical intensity 52 is an optical intensity of the light that reaches the light receiving element 16. The monitor optical intensity 52 correlates with an output from the semiconductor laser 10. The light receiving element 16 outputs the monitor optical intensity 52 to an output controller 20, as monitor optical intensity information 62.
The output controller 20 externally obtains output control information 60, which represents a demand of the optical output intensity 50 desired by the user, and also obtains the monitor optical intensity information 62 from the light receiving element 16. The output controller 20 calculates a drive current 66 to be output to the semiconductor laser 10 with the output control information 60 and the monitor optical intensity information 62 so as to set the optical output intensity 50 at a desired value. The drive current 66 is output to the semiconductor laser 10. Even if the output from the semiconductor laser 10 is changed, the optical output intensity 50 is kept constant. In this manner, Auto Power Control (APC) is to control the optical output intensity 50 at a desired value with the use of the monitor optical intensity information 62.
The other split beam reaches a wavelength detector 28. The wavelength detector 28 includes an etalon 24 and a light receiver 26. The beam that passes through the etalon 24 has a correlation value of wavelength—optical intensity. The light receiver 26 outputs the value having a correlation between wavelength and optical intensity that has passed the etalon 24, to a wavelength controller 30 as wavelength information 72.
With the use of the wavelength information 72, the wavelength controller 30 outputs setting temperature information 74 to the temperature setting apparatus 32 in order to set the wavelength at a desired value. This is accomplished by measuring, in advance, the wavelength information 72 and the setting temperature information 74 at the time when the desired wavelength is detected, prior to the shipment of the semiconductor laser module having the wavelength locker, and by providing a tuning table having the temperature setting information 74 that corresponds to the wavelength information 72. The temperature setting apparatus 32 sets the semiconductor laser 10 at a given temperature according to the temperature setting information 74. In this manner, according to the conventional art, the temperature of the semiconductor laser 10 is controlled to obtain a desired wavelength.
As described heretofore, according to the conventional art. Even if the temperature of the semiconductor laser 10 changes and the optical output from the semiconductor laser 10 changes, the light receiving element 16 receives a portion of the output from the semiconductor laser 10, and feedbacks the monitor optical intensity information 62 to the drive current 66 in order to obtain a desired wavelength, in other words, APC is accomplished. Thus, the optical output intensity can be stabilized at a given value.
As a method of correcting the change in the optical output intensity caused by the change in the temperature of the module having the semiconductor laser, there are additional conventional arts. One example is disclosed in Japanese Patent Application Publication No. 5-312646, in which a laser module having a semiconductor laser that detects the temperature of an etalon and corrects the wavelength. Another example is disclosed in Japanese Patent Application Publication No. 8-139395, in which a laser module having a semiconductor laser that detects the temperature of the semiconductor laser to prevent the change of a laser beam output intensity due to the temperature of the semiconductor laser or ambient temperature.
The conventional arts, however, have the problem in that the optical output intensity of a desired value is not available. FIG. 3 is a graph showing the afore-mentioned problem. In FIG. 3, the horizontal axis represents the output wavelength, and the vertical axis represents the optical output intensity. As described, according to the conventional arts, the wavelength is controlled by controlling the temperature of the semiconductor laser 10. That is to say, the wavelength on the horizontal axis corresponds to the temperature. Although the monitor optical intensity 52 controls the output from the semiconductor laser 10 (APC control), the optical output intensity 50 changes as the wavelength changes, in other words, the temperature changes. Under such circumstances, the semiconductor laser module cannot serve as a high-quality one for use in optical communication.